Infrared transceivers that conform to specifications known as IrDA (Infrared Data Association) are typically used in portable electronic devices, such as personal digital assistants (PDAs), cell phones, pagers, digital cameras, portable MP3 players and laptop computers. The IrDA specifications call for infrared signals having wavelengths approximately in the range of 850 nm to 900 nm (for example, 875 nm). Transmitters used in remote control devices that control electronic consumer devices typically transmit remote control infrared signals. Remote control devices typically use infrared signals with wavelengths approximately in the range of 900 nm to 1000 nm (for example, 940 nm). In addition to the IR wavelength, the transmission protocols for IrDA signals and remote control infrared signals are very different. Although the various manufacturers of electronic consumer devices use different coding and modulation schemes to control their electronic consumer devices, the signals used to control all such electronic consumer devices are referred to here as “RC” infrared signals. RC infrared signals typically control electronic consumer devices such as televisions, stereo radios, digital video disc players, video cassette recorders, set-top cable television boxes and set-top satellite boxes.
A transmitter that can emit both IrDA signals and RC infrared signals could be used in both portable electronic devices as well as remote control devices. In addition, a portable electronic device containing a transmitter that can transmit both IrDA signals and remote control infrared signals can be used to control electronic consumer devices. For example, an 875 nm IrDA transmitter light-emitting diode (LED) could be used as to transmit both IrDA signals and RC infrared signals. Although the peak wavelength of the 875 nm IrDA transmitter LED and the wavelength of peak sensitivity of a remote control receiver are not matched, radiation emitted by the 875 nm transmitter LED is nevertheless received by the remote control receiver. Generating IrDA signals and RC infrared signals with one transmitter LED, however, presents technical difficulties.
First, due to the mismatch between peak IrDA transmission wavelength and peak RC reception sensitivity, it may be necessary to increase the power to the IrDA transmitter LED to achieve sufficient reception by the remote control receiver. The increased power consumption of the IrDA transmitter LED reduces battery life. A portable electronic device with a longer battery life, however, is more attractive to consumers. Being able to extend battery life is very valuable. Battery life is therefore often a very important design consideration for portable electronic devices, such as personal digital assistants (PDAs). Thus, a technique is sought whereby power consumption in a combined IrDA/remote control transceiver can be reduced.
Second, the cost of portable electronic devices is also an important consideration for consumers. Driving down the manufacturing cost of the PDA, and the combined IrDA/remote control transceiver within the PDA, is an important objective. A method and structure for reducing manufacturing costs of price-sensitive portable electronic devices, such as PDAs, that generate both IrDA signals and RC infrared signals is desired.